Centrifugal gas compressors have long been employed for many purposes, including applications as diverse as jet engines and heat pumps. Previous developments relating to centrifugal gas compressors have shown that the injection of vaporizable liquid into the gas stream of the compressor to achieve wet compression, or compression involving vaporization of the injected liquid, as opposed to dry compression, is particularly advantageous. This is because vaporization of injected liquid in the compressor reduces the inlet temperature of the compressor stage downstream of the liquid injection point, thereby resulting in a significant increase in compression ratio, or ratio of output gas pressure to input gas pressure, for little or no increase in power supplied to the compressor. Additionally, the operating temperature of the compressor may be effectively reduced by direct water injection, thereby eliminating the need for expensive external intercoolers.
Although the benefits obtained by injecting vaporizable liquid directly into the gas stream of a centrifugal compressor are widely recognized, the devices and techniques known to the prior art for providing wet compression have posed some distinct disadvantages. A reference typifying such prior art is U.S. Pat. No. 2,786,626 to Redcay. Redcay discloses a process for the compression of gas in a multistage compressor wherein vaporizable liquid is injected into the compressor inlet and is also injected into the cross-over channel of each of the first several compressor stages. The liquid injected into the cross-over channels is injected through liquid jets, only one per stage, oriented upstream of the gas stream of the compressor.
The compressor of Redcay suffers from achieving a rather limited degree of vaporization of the liquid injected into the compressor gas stream. This is because the liquid is injected into a low velocity region of the compressor and thus the breaking up or atomizing of the liquid into very small droplets is not achieved. This is particularly so in regard to the liquid injected into the compressor inlet. Very small droplets are necessary to achieve a high degree of vaporization because the surface area of such a droplet is large relative to the volume of the droplet, and the droplet can thus readily absorb heat and vaporize. The limited vaporization of the injected liquid in the Redcay compressor results in a limited reduction in power required for his compressor. The limited vaporization also results in large liquid droplets impinging on internal compressor parts, such as the impeller, thus posing a definite risk of serious erosion and pitting of these parts after a relatively short period of operation.
If it is desired to inject liquid from the jets of Redcay into the compressor gas stream an adequate distance to attain a reasonable degree of atomization thereof, his compressor would suffer from requiring complex apparatus for injecting the liquid into the gas stream at high velocity. Such high velocity is necessary, owing to the fact that his liquid jets are oriented against the direction of flow of the gas stream.